Quantity and quality of soil organic matter as a sustainability index under different land uses in Eastern Amazon

ABSTRACT: Soil organic matter (SOM), which influences chemical, physical and biological soil attributes, is the main form of C found in the soil which can also be used as a soil sustainability index. The aim of this study was to use the quantity and quality of SOM as an indicator to determine the sustainability of different land uses (native vegetation, secondary vegetation, fruit orchards, horticultural areas, degraded pasture, improved pasture, and fields with annual crops) in the eastern Amazon. Improved pasture had higher soil C stock than the other land uses and was similar to the native vegetation, and also presented the highest quantity of C in a stable form in the soil (fraction < 53 μm). According to the C management index, improved pasture is the most similar in use to native vegetation. Changes in land use reduced the soil microbial C content, although the more conservationist systems (fruit orchards, secondary vegetation, and improved pasture) had contents similar to those of the native vegetation. The highest soil microbial quotients were found in fruit orchards and horticultural areas. Well-managed pastures were effective in accumulating C as stable forms in the soil, which demonstrates the sustainability of this land use in the region studied.

摘要：土壤有机质（Soil organic matter, SOM）可影响土壤的化学、物理及生物学属性，是土壤中碳（C）的主要赋存形式，同时也可作为土壤可持续性评价指标。本研究以土壤有机质的数量与质量为指标，旨在评估亚马孙东部地区不同土地利用方式的可持续性，涵盖原生植被、次生植被、果园、园艺种植区、退化牧场、改良牧场及一年生作物田7类用地。研究结果显示，改良牧场的土壤碳储量高于其余所有土地利用类型，且与原生植被水平相当；同时其土壤中稳定态碳（粒径<53 μm的组分）含量最高。依据碳管理指数，改良牧场的土地利用模式与原生植被最为相似。土地利用方式的改变会降低土壤微生物碳含量，但保护性更强的用地系统（果园、次生植被与改良牧场）的土壤微生物碳含量与原生植被相近。果园与园艺种植区的土壤微生物熵值最高。管理得当的牧场可有效积累土壤稳定态碳，这证实了该土地利用方式在本研究区域内具备可持续性。